1. Field of the Invention
This invention relates to an improvement in a fluid coking process. It particularly relates to an improvement in the elutriation of the circulating coke. More particularly, it relates to an improvement in the elutriation of coke in an integrated fluid coking and coke gasification process.
2. Description of the Prior Art
Integrated fluid coking and gasification processes are known. See, for example, U.S. Pat. Nos. 3,661,543, 3,816,084; 3,702,516; and 3,779,900, the teachings of which are hereby incorporated by reference. In such integrated processes, at least a portion of the coke product is gasified by reaction with steam and an oxygen-containing gas to produce a hydrogen-containing fuel gas. The hot gasifier effluent including entrained solids is introduced into a heating zone to provide at least a portion of the heat required to heat relatively colder coke particles in a fluidized bed of coke.
In the conventional fluid coking process, such as disclosed in U.S. Pat. No. 2,881,130, the teachings of which are hereby incorporated by reference, a stream of coke is circulated to a burner in which a portion of the coke is burned to provide the heat requirements of the process. Although a large number of coke agglomerates are produced in the coking reactor, some of these agglomerates disintegrate in the burner and a large portion of agglomerates is withdrawn with the product coke. Therefore, in the conventional fluid coking process, the concentration of agglomerates in the system remains relatively low. In contrast, in the integrated fluid coking and coke gasification process, the rate of withdrawal of product coke is low, and therefore the accumulation of agglomerates becomes a problem. Although there is a substantial increase in the deagglomeration process due to the gasification of a large portion of the gross coke, it is not adequate to purge the agglomerates from the circulating coke. The problem of removing enough agglomerates from the system while maintaining a particle size distribution suitable for good fluidization in the coke circulation lines had to be overcome. One way of improving the agglomerate withdrawal is to provide an improved method of elutriation of the coarse particles. Another problem that occurs in the integrated fluid coking and coke gasification process is the distribution of the hot, corrosive, gasification zone gaseous effluent which contains some entrained coke, into the heating zone bed. To reduce the temperature of the hot gasifier effluent, it had been proposed to mix a colder stream of coke with the hot gas (see, for example, U.S. Pat. Nos. 3,702,516 and 3,779,900). Although the proposed methods could reduce the temperature of the gas, these methods still did not solve the problem of elutriating the coke particles from the gasifier effluent and of operating at normal loading and velocity while maintaining a velocity where slugging would not be a problem during turndown. Another problem which had to be solved was a method whereby a rapid rise in temperature in the riser of the heater would not occur when the quench coke circulation stops.
It has now been found that these difficulties can be overcome by the process of the present invention whereby the quenched gasification effluent is elutriated in the heating vessel riser prior to introducing the solids-containing gaseous stream into the main heat exchange zone of the heating vessel.